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Physiological diversity and temperature hardening in adult tick Dermacentor variabilis (Acari: Ixodidae) [electronic resource] /

by Hwang, Kai-Lun Hsu

Abstract (Summary)
Abstract: Ticks employ an array of survival traits in response to adverse environmental conditions including behavior, active water-vapor uptake, integumental restriction of water loss, slow metabolism/respiration, and tolerance of temperature extremes. This dissertation studied the rapid heat hardening and rapid cold hardening traits, which increase tolerance to temperature extremes in Dermacentor variabilis. An unexpected physiological diversity was found in our studies, which added an interesting dimension to the project. Ultimately, survival experiments demonstrated that there was a seasonal (summer vs. winter) or 'batch' effect, apparently caused by when ticks were laboratory reared. In high temperature (45 °C) survival studies, high and low temperature cross-tolerance was ambiguous in summer-acclimated ticks whereas it was clearly demonstrated in winter-acclimated ticks. Likewise, in low temperature (-10 °C) survival studies, the high and low temperature cross-tolerance was clearly demonstrated in summer ticks, but not in winter ticks. Seasonal acclimation seems to play a principle role, while rapid hardening adds supplemental benefits by protecting D. variabilis against high and low temperature injuries. Two clones of Hsp70 were identified and characterized in D. variabilis and named Hsp70S (short form, 1540 bp) and Hsp70L (long form, 1727 bp). Hsp70S and Hsp70L share 95% nucleic acid sequence identity with the differences at their 3' ends. They share 81% nucleic acid identity and 87% amino acid similarity with an Hsp70 of the deer tick, Ixodes scapularis. The Northern expression of Hsp70S was much higher compared to Hsp70L in response to high temperature exposures. Synthesis of Hsp70 in response to cold- and desiccation-acclimation was slight and delayed. Neither the field collected natural population (in summer) nor the outdoor acclimated (in winter) lab-reared ticks showed any higher level of Hsp70 expression than the controls. Rapid hardening correlates with concomitant increases in hemolymph osmotic pressure, glycerol and sorbitol concentrations in D. variabilis. Glycerol plays a significant protective role for D. variabilis against low and high temperature injuries. Sorbitol might play a secondary role, but its concentration is only thousandth of glycerol. This study increases our understanding of this tick's survival traits and helps explain its impressive diversity in northern temperate America.
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Advisor:

School:The Ohio State University

School Location:USA - Ohio

Source Type:Master's Thesis

Keywords:american dog tick

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